<template>
  <ul class="list">
    <li class="item" v-for="item of letters" :key="item"
     @click="handleLetterClick"
     @touchstart.prevent="handleTouchStart"
     @touchmove="handleTouchMove"
     @touchend="handleTouchEnd"
     :ref="item"
     >
      {{item}}
    </li>
  </ul>
</template>

<script>
export default {
  name: 'CityAlphabet',
  props:{
    cities:Object
  },
  computed:{
    letters(){
      const letters=[];
      for(let i in this.cities){
        letters.push(i)
      }
      return letters;
    }
  },
  updated(){
    this.startY = this.$refs['A'][0].offsetTop
  },
  data(){
    return{
      touchStatus:false,
      startY:0,
      timer:null
    }
  },
  methods:{
    handleLetterClick(e){
      this.$emit('change',e.target.innerText);  
    },
    handleTouchStart(){
       this.touchStatus=true;
    },
    handleTouchMove(e){
      if(this.touchStatus){ 
        if(this.timer){
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(()=>{
           const touchY = e.touches[0].clientY -79
            const index =Math.floor((touchY - this.startY)/20)
            if(index>=0&&index<this.letters.length){
              this.$emit('change',this.letters[index]);
            }
 
        })
           
        
     
      }
    },
    handleTouchEnd(){
      this.touchStatus=false;
    }
  }
 
}
</script>
<style lang="less" scoped>
 @import '~styles/varibles.less';
.list{
  display:flex;
  flex-direction:column;
  justify-content:center;
  position:absolute;
  top:1.58rem;
  right:0;
  bottom:0;
  width:0.4rem;
  .item{
    text-align:center;
    line-height:0.4rem;
    color:@bgColor;
  }
}
</style>